How can I combine two separate object?
First, select both objects, and press Ctrl+J. Then, go into Edit Mode, select the both rings of vertices on the ends of the gap, press W and then select Bridge Edge Loops.  

In order to have different texturing for different parts, you'll need to make the different textures into different materials, (so if you want two textures, you'll make two textures,) and then, select vertices you want the material to be put on, select the material you want to put on them, and press the Assign button, which is under the material name.

Read: Add different materials to different parts of a mesh? (frequently asked question)